The present invention relates to a cord drive for producing rotary motion. In the embodiments shown here, the cord drive is used for raising and lowering coverings for architectural openings such as Venetian blinds, pleated shades, and other blinds and shades. This cord drive may also be used on vertical blinds and other mechanical devices requiring rotary motion.
Typically, a blind transport system will have a top head rail which both supports the blind and hides the mechanisms used to raise and lower or open and close the blind. Such a blind system is described in U.S. patent application Ser. No. 09/528,951, filed Mar. 20, 2000, which is hereby incorporated by reference. The raising and lowering is done by a lift cord attached to the bottom rail (or bottom slat). The opening and closing of the blind is typically accomplished with ladder tapes (and/or tilt cables) which run along the front and back of the stack of slats. The lift cords (in contrast to the tilt cables) may either run along the front and back of the stack of slats or they may run through slits in the middle of the slats, and are connected to the bottom rail.
A wide variety of drive mechanisms is known for raising and lowering blinds and for tilting the slats. A cord drive to raise or lower the blind is very handy. It does not require a source of electrical power, and the cord may be placed where it is readily accessible, getting around any obstacles.
In prior art cord drives used for blinds, it is typical for the same cord to be used to drive the lift action and to extend through the slats and fasten to the bottom slat (or bottom rail) to lift the blind.
Known cord drives have some drawbacks. The cords in a cord drive, for instance, may be such that they are either hard to reach when the cord is way up (and the blind is in the fully lowered position), or the cord may drag on the floor when the blind is in the fully raised position. Also, for heavy blinds, a large force may be required on the cord in order to lift the blind.
The present invention provides a cord drive which has the advantages of prior art cord drives, plus it eliminates many of the problems of prior art cord drives. One preferred embodiment of the present invention provides a cord drive which does not require the drive cord to travel as far as the lift cord. It also permits the use of a drive cord loop, which always has the same exposed length regardless of the position or length of the blind.
Note that, for the purposes of this description, we will hereafter refer to two drive cords, each having one end mounted on the cord drive. However, it should be understood that the language referring to two drive cords includes the situation in which the two drive cords are connected together to form a loop so that they are, in effect, a single cord having one end mounted on each spool of the cord drive.
In the present invention, the drive cord in the cord drive is a totally different cord from the lift cord which attaches to the bottom rail.
An objective of the present invention is to have a simple wind up spool system with a minimum of moving parts, which will consistently and reliably wind and unwind the drive cords without jamming or over-wrapping, and with the ends of the drive cords exiting the cord drive always at the same location instead of moving along the length of the wind up spool.
To accomplish these goals, a preferred embodiment of the cord drive includes two spools which rotate as a single piece. The drive cords are counter-wrapped onto the spools such that, as both spools rotate in the same direction, one cord is unwinding from its respective spool, while the second cord is winding onto its spool. Finally, the spools have a slight taper at the inlet end, where the drive cords are first wrapped onto the spools, and the cord drive includes a cover which not only accurately positions the cords onto the tapered section of the spools: it also has a clearance of less than twice the diameter of the drive cord between the outer tapered surface of the spool and the inner surface of the cover. Thus, as the cord is placed onto the tapered surface of the spool, the drive cord wraps are displaced axially along the length of the spool and down the tapered surface of the spool, and the clearance will not allow an over-wrap condition to occur. The cover may also provide support for the spools; it may guide the drive cords so they exit the cord drive at the same location all the time; and it may also provide a mounting mechanism to mount the cord drive to the head rail.
When the cord drive is used for a blind, the drive spools may be connected to the rest of the blind mechanism by means of a lift rod or drive shaft. In fact, the lift rod may be the mechanism linking the two spools together so that they rotate as a single unit, as is the case in some preferred embodiments. Then, as a drive cord end is pulled in the cord drive mechanism, it unwinds from a first spool and makes this first spool rotate. The rotation of this first spool causes the lift rod to rotate which causes a second spool to rotate, thus causing the other drive cord to counter-wrap onto this second spool. The rotation of the lift rod may also cause a lift station to rotate, winding or unwinding the lift cord to raise or lower the blind, depending on the direction of rotation.
While the present invention is shown being used in a typical horizontal Venetian blind, it should be obvious to those skilled in the art that this cord drive may be used in any number of different types of mechanical drives.